Working with Arrays

Len KamermanInstructorCS-10001, Mohawk College, Fall 2010

Agenda

What Is An Array?Using Arrays With GMLWhen Are They Useful?A SampleGive Yourself Arrays (sample problem)

One array can hold MULTIPLE values

What is an array?

An array is a COLLECTION of data itemsMost variables hold a SINGLE value

380True“Apple”

“Apple”

“Cherry”

“Grape”

380

27

60

217

What is an array?

Arrays follow variable naming rulesBut they also have an INDEXThe INDEX refers to a particular value in the array

“Apple”

“Cherry”

“Grape”

FruitNames

012

Indexes ->

What is an array?

If a regular variable is like a house… Then an array is like a condo…

They all share one common address (variable name) but they each have their own apartment number (an INDEX)

Think of an INDEX like an apartment number

What is an array?

NOTE: the first INDEX is 0, not 1This is the case is most programming languages!

“Apple”

“Cherry”

“Grape”

FruitNames

012

Indexes ->

Using Arrays with GMLIn GML, you do not need to declare arraysAn array in GML looks like this:

VarName[index]

VarName is the variable nameindex is an integer

Examples:strSubject[0] = “History”;strSubject[1] = “Math”;

Using Arrays with GML – Try This!

Create a script in GMLCreate an array with three values:strPop[0] = “Pepsi”;strPop[1] = “7-Up”;strPop[2] = “Dr. Pepper”;Print each to the screen with a message box:show_message(strPop[0]);show_message(strPop[1]);show_message(strPop[2]);

When Are They Useful?

When you’d like to store similar related valuesstrCookie[0] = “Chocolate Chip”;strCookie[1] = “Oatmeal”;strCookie[2] = “Anchovy”;strCookie[3] = “Peanut Butter”;

When Are They Useful?

When you need to store many values

var num1, num2, num3, num4, num5, num6, num7, num8, num9, num10, num11……

num[0] = 7;num[1] = 5;num[2] = 6;…num[10] = 4;

When Are They Useful?

Process multiple values within a REPITITION structure (if you like loops, you’ll love arrays!)With the use of a counter, each iteration processes the next value

x[0] = 1;x[1] = 7;x[2] = 4;for (i = 0; i < 3; i++){

total = total + x[i];}

When Are They Useful? – Try This!

Using our same array of brands/kinds of pop:strPop[0] = “Pepsi”;strPop[1] = “7-Up”;strPop[2] = “Dr. Pepper”;for (i = 0; i < 3; i = i + 1){

show_message(strPop[i]);}

A SampleHave the user enter as many numbers as they likeWhen they want to quit entering numbers, they enter -99After they finish entering numbers:

show them all the numbers they entereddetermine which number is the biggest and display it

A Samplevar user_number, numbers, counter, biggest;user_number = get_integer(“Enter a number”, 0);biggest = 0;counter = 0;while (user_number != -99){ numbers[counter] = user_number; counter = counter + 1; user_number = get_integer(“Enter a number”, 0);}for (i = 0; I < counter; I = I + 1){ show_message(string(numbers[i])); if (numbers[i] > biggest) biggest = numbers[i];}show_message(string(biggest) + “ was the largest number”);

Give Yourself Arrays – Sample 1

Prompt the user for three numbers and store them in an arrayUse a loop to put the numbers together in a stringE.g., if your numbers are 12, 57, and 42, combine them into a string to give “125742”Display this string in a message box

Give Yourself Arrays – Sample 2

Write a script to ask the user for a lunch orderPrompt them to enter each item, for example:

hotdogchipsCoke

When they are done entering items, they should enter the word “nothing”Display each item in their lunch order in the reverse order they entered them